In a mobile communication system, use of a femtocell lower than a so-called macro cell in transmission power is expanded with the object of efficiently using radio resources, eliminating a radio wave dead zone, reducing the cost of developing an area, and improving communication quality. To improve the communication quality, in a mobile communication system in which the above-described macrocell and femtocell are mixed, it is preferred that if possible, a mobile terminal is present in a femtocell and performs communication. In order that more mobile terminals may be present in a femtocell, it is considered, for example, that transmission power of the femtocell is increased and a cell radius is expanded.
In a mobile communication system in which a macrocell and a femtocell use the same frequency band, however, radio waves transmitted from each of the macrocell and femtocell interfere with each other, and as a result communication quality of the other side is deteriorated. Particularly, when transmission power is increased to improve communication quality of the femtocell as described above, interference which exerts an influence on communication of a macrocell and other femtocells located on the periphery of the femtocell may increase.
In a citation list as indicated below, for example, there will be described a technique for solving a technical problem according to deterioration of communication quality due to interference between a macrocell and a femtocell. In the following citation list, a technique will be described such that when transmission power of a femtocell which refuses a handover request from a mobile terminal is decreased and a cell radius is reduced, interference to a mobile terminal which is present in a cell being a handover request source is suppressed.
Japanese Laid-open Patent Publication No. 2010-16420
However, with regard to techniques which are described in the above-described citation list, problems described below are left. When transmission power of a femtocell is decreased in handover operations of one mobile terminal, an influence is exerted on interference to the other mobile terminals connected to the femtocell and an interference amount is increased. As a result, communication speed of mobile terminals is reduced and communication is disabled.
On the other hand, more mobile terminals are also requested to be present in a femtocell. During handover operations, when transmission power of a femtocell is increased and a cell radius is expanded, there is an advantage that a mobile terminal preferably hands over to the femtocell and starts communication.